Friction characteristics of piston rings in a free-piston engine generator

2016 ◽  
Vol 18 (9) ◽  
pp. 871-885 ◽  
Author(s):  
Chenheng Yuan ◽  
Jing Xu ◽  
Huihua Feng ◽  
Yituan He
Keyword(s):  
Friction Model ◽  
Piston Engine ◽  
Piston Rings ◽  
Coupled Models ◽  
Free Piston ◽  
Friction Characteristics ◽  
Friction Power ◽  
Reciprocating Engine ◽  
Free Piston Engine ◽  
Insight Into

Free-piston engine generator is a new alternative to traditional reciprocating engine, which moves without mechanical restriction of crankshaft system. This article investigated numerically the friction characteristics of piston rings in a free-piston diesel engine generator by adopting coupled models of dynamic and friction. The development of the dynamic model and friction model was described, and an iterative calculation method was presented, giving insight into the coupled parameters of these two models. The detailed effects of the dynamic on friction and lubrication were investigated compared with a corresponding traditional crank engine. The friction characteristics of the free-piston engine generator were found to differ clearly from those of the traditional engine due to its special piston motion. Compared with the traditional engine, the minimum lubricant film thickness of piston rings in the free-piston engine generator is thicker and lasts shorter at the dead center regions, but it is generally thinner at other positions. The average friction force, friction power, and friction work of the piston rings in the free-piston engine generator are less than the traditional engine due to the better lubrication in endpoints region. Meanwhile, the friction power of the free-piston engine generator increases with the increase in fuel mass or decrease in load. The friction efficiency varies in correlation with the generator load; the optimum friction efficiency can be obtained by either increasing or decreasing from a certain generator load.

Thermodynamic Simulation and Prototype Testing of a Four-Stroke Free-Piston Engine

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
Jiming Lin ◽  
Zhaoping Xu ◽  
Siqin Chang ◽  
Ningxia Yin ◽  
Hao Yan
Keyword(s):  
Thermodynamic Simulation ◽  
Thermodynamic Cycle ◽  
Energy Conversion Efficiency ◽  
Piston Engine ◽  
Free Piston ◽  
Free Piston Engine ◽  
Simulation And Experiment ◽  
Intake Stroke ◽  
Engine System ◽  
Insight Into

In order to achieve higher-energy conversion efficiency, a free-piston engine with an improved four-stroke thermodynamic cycle is investigated in this paper. This cycle is optimized according to the variable strokes feature and is characterized by the short intake stroke, the complete expansion stroke, the external pressurization, and the intercooling. The development of a four-stroke free-piston engine system simulation model was described, and the effects of the cycle on the system performances were qualitatively analyzed. According to the experiment of the prototype, the generating efficiency of 33.4% can be achieved when the system is fueled with gasoline and the output power is significantly increased from 1.62 to 2.68 kW. The simulation and experiment results are analyzed in detail, giving insight into the performances of the system. Studies show that the energy-saving and environmental protection performances of the system can be significantly promoted by using the improved thermodynamic cycle.

In-cylinder heat transfer and gas motion of a free-piston diesel engine generator

2017 ◽  
Vol 231 (8) ◽  
pp. 739-752 ◽  
Author(s):  
Chenheng Yuan ◽  
Jing Xu ◽  
Huihua Feng
Keyword(s):  
Heat Transfer ◽  
Gas Flow ◽  
Attractive Alternative ◽  
Piston Engine ◽  
Piston Motion ◽  
Compression Process ◽  
Free Piston ◽  
Reciprocating Engine ◽  
Free Piston Engine ◽  
Significant Difference

The free-piston engine generator is an attractive alternative to the conventional reciprocating engine due to the feature that it moves without crankshaft system. This paper presented a simulation for the investigation on the characteristic of in-cylinder gas motion and heat transfer in a compression ignited free-piston engine generator. An operation experiment was performed to obtain the precise piston motion for the modeling of heat transfer and gas flow. The development of the multi-dimensional model was described, and simulation results were presented and showed good similarity with the experimental data. Then, the heat transfer and gas motion in the free-piston engine generator were discussed, on which the influences of piston motion were also investigated compared with a corresponding conventional reciprocating engine. The results indicated that compared with the conventional reciprocating engine, a higher level of squish and reverse squish effect was found for the free-piston engine generator due to its faster motion around top dead center, while its slower piston motion led to weaker gas turbulence in the compression process. Moreover, the free-piston engine generator and conventional reciprocating engine did not show a significant difference in heat transfer during the compression process, however, an obvious advantage of heat transfer was indicated for the free-piston engine generator in combustion and expansion processes due to its lower combustion temperature and the reduced time that is available for heat transfer caused by its faster expansion. The mechanism for such differences is that the free-piston engine generator moves with uneven equivalent speed.

Tribological characteristics of piston rings in a single-piston hydraulic free-piston engine

2017 ◽  
Vol 69 (2) ◽  
pp. 131-141 ◽  
Author(s):  
Zhaoju Qin ◽  
Chenheng Yuan ◽  
Yanpeng Yuan ◽  
Yuanyuan Huang
Keyword(s):  
Numerical Simulation ◽  
Friction Loss ◽  
Piston Engine ◽  
Piston Motion ◽  
Piston Rings ◽  
Free Piston ◽  
Content Type ◽  
Compression Stroke ◽  
Free Piston Engine ◽  
Loss Efficiency

Purpose A free-piston engine (FPE) is an unconventional engine that abandons the crank system. This paper aims to focus on a numerical simulation for the lubricating characteristics of piston rings in a single-piston hydraulic free-piston engine (HFPE). Design/methodology/approach A time-based numerical simulation program was built using Matlab to define the piston motion of the new engine. And a lubrication mode of piston rings was built which is based on the gas flow equation, hydrodynamic lubrication equation and the asperity contact equation. The piston motion and the lubrication model are coupled, and then the finite difference method is used to obtain the piston rings lubrication performances of the FPE. Meanwhile, the lubrication characteristics of the new engine were compared with those of a corresponding conventional crankshaft-driven engine. Findings The study results indicate that compared with the traditional engine, the expansion stroke of the HFPE is longer, and the compression stroke is shorter. Lubrication oil film of the new engine is thicker than the traditional engine during the initial stage of compression stroke and the final stage of the power stroke. The average friction force and power of the hydraulic free piston engine are slightly lower than those of the traditional engine, but the peak friction power of the FPE is significantly greater than that of the traditional engine. With an increase in load, the friction loss power and friction loss efficiency decrease, and with a decrease in equivalence ratio, the friction power loss reduces, but the friction loss efficiency decreases first and then increases. Research limitations/implications In this paper, only qualitative analysis was performed on the tribological difference between conventional crankshaft engine and HFPE, instead of a quantitative one. Practical implications This paper contributes to the tribological design method of HFPE. Social implications No social implications are available now, as the HFPE is under the development phase. However, the authors are positive that their work will be commercialized in the near future. Originality/value The main originality of the paper can be introduced as follows: the lubrication and friction characteristics of the new engine (HFPE) were investigated and revealed, which have not been studied before; the effect of the HFPE’s special piston motion on the tribological characteristics was considered in the lubrication simulation. The results show that compared with the traditional crankshaft engine, the new engine shows a different lubrication performance because of its free piston motion.

scholarly journals Research on the Operating Characteristics of Hydraulic Free-Piston Engines: A Systematic Review and Meta-Analysis

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3530
Author(s):  
Fukang Ma ◽  
Shuanlu Zhang ◽  
Zhenfeng Zhao ◽  
Yifang Wang
Keyword(s):  
Systematic Review ◽  
High Efficiency ◽  
Meta Analysis ◽  
Combustion Process ◽  
Research Progress ◽  
Future Research ◽  
Operating Characteristics ◽  
Piston Engine ◽  
Free Piston ◽  
Free Piston Engine

The hydraulic free-piston engine (HFPE) is a kind of hybrid-powered machine which combines the reciprocating piston-type internal combustion engine and the plunger pump as a whole. In recent years, the HFPE has been investigated by a number of research groups worldwide due to its potential advantages of high efficiency, energy savings, reduced emissions and multi-fuel operation. Therefore, our study aimed to assess the operating characteristics, core questions and research progress of HFPEs via a systematic review and meta-analysis. We included operational control, starting characteristics, misfire characteristics, in-cylinder working processes and operating stability. We conducted the literature search using electronic databases. The research on HFPEs has mainly concentrated on four kinds of free-piston engine, according to piston arrangement form: single piston, dual pistons, opposed pistons and four-cylinder complex configuration. HFPE research in China is mainly conducted in Zhejiang University, Tianjin University, Jilin University and the Beijing Institute of Technology. In addition, in China, research has mainly focused on the in-cylinder combustion process while a piston is free by considering in-cylinder combustion machinery and piston dynamics. Regarding future research, it is very important that we solve the instabilities brought about by chance fluctuations in the combustion process, which will involve the hydraulic system’s efficiency, the cyclical variation, the method of predicting instability and the recovery after instability.

A review on the operating characteristics of free piston engine and its recent developments

2018 ◽  
Author(s):  
Evelyn Evelyn ◽  
A. Rashid A. Aziz ◽  
Firmansyah Firmansyah ◽  
Ezrann Zharif Zainal Abidin
Keyword(s):  
Operating Characteristics ◽  
Piston Engine ◽  
Free Piston ◽  
Free Piston Engine ◽  
Recent Developments
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